The invention relates to interconnection between integrated circuit devices and other similar devices or test structures used for burn-in or evaluation of the devices. More specifically, the invention relates to geometrical arrays of contacts, distributed through flexible films and elastomers to establish reliable, low force electrical interconnection between electronic components.
The introduction of solid-state semiconductor electronics provided the opportunity for progressive miniaturization of components and devices. One of the benefits of such miniaturization is the capability of packing more components into a given space. This increases the features, versatility and functionality of an electronic device, usually at lower cost. A drawback of such advances is the reduction in spacing between contacts on one device and the need for accurate alignment with corresponding contacts on a second device to provide reliable electrical interconnection between the two. Modern technology, using VLSI electronics, challenges design engineers to provide such fine interconnection structures that electrical isolation between individual connectors becomes a primary concern. Current designs, for example, include spaces as low as 0.15 mm between contacts. Secondary to connector isolation is the inevitable reduction in pliability of insulating material, between electrical contacts, as the distance between contacts decreases. Thus, a geometrical array of contacts held together by a planar insulating material allows less independent movement between contacts the closer they approach each other. Absent freedom of movement, individual contacts may fail to connect to a target device, especially if some of the device contacts lie outside of a uniform plane. Lack of planarity causes variation in the distance between the device contacts and an array of contacts intended to mate with the device contacts. Accurate engagement by some contacts leaves gaps between other contacts unless independent contacts have freedom to move across such gaps. Alternatively the connecting force between an array of contacts and device contacts must be increased, for reliable interconnection, with resulting compression and potential damage for some of the contacts.
Interconnection of electronic components with finer and finer contact spacing or pitch has been addressed in numerous ways along with advancements in semiconductor device design. Introduction of ball grid array (BGA) devices placed emphasis on the need to provide connector elements with space between individual contacts at a minimum. One answer, found in U.S. Pat. Nos. 5,109,596 and 5,228,189, describes a device for electrically connecting contact points of a test specimen (circuit board) to the electrical contact points of a testing device using an adapter board having a plurality of contacts arranged on each side thereof. Cushion-like plugs made from an electrically conductive resilient material are provided on each of the contact points to equalize the height variations of the contact points of the test specimen. An adapter board is also provided made of a film-like material having inherent flexibility to equalize the height variations of the contact points of the test specimen. Furthermore, an adapter board is provided for cooperating with a grid made of an electrically insulated resilient material and having a plurality of plugs made from an electrically conductive resilient material extending therethrough. Successful use of this device requires accurate registration of contacts from the test specimen, through the three layers of planar connecting elements to the testing device.
U.S. Pat. Nos. 5,136,359 and 5,188,702 disclose both an article and a process for producing the article as an anisotropic conductive film comprising an insulating film having fine through-holes independently piercing the film in the thickness direction, each of the through-holes being filled with a metallic substance in such a manner that at least one end of each through-hole has a bump-like projection of the metallic substance having a bottom area larger than the opening of the through-hole. The metallic substance serving as a conducting path is prevented from falling off, and sufficient conductivity can be thus assured. While the bump-like projections of the anisotropic conductive films, previously described, represent generally rigid contacts, U.S. Pat. Nos. 4,571,542 and 5,672,978 describe the use of superposed elastic sheets over a printed wiring board, to be tested, and thereafter applying pressure to produce electroconductive portions in the elastic sheet corresponding to the contact pattern on the wiring board under test. In another example of a resilient anisotropic electroconductive sheet, U.S. Pat. No. 4,209,481 describes a non-electroconductive elastomer with patterned groupings of wires, electrically insulated from each other, providing conductive pathways through the thickness of the elastomer. Other known forms of interconnect structure may be reviewed by reference to United States Patents including U.S. Pat. Nos. 5,599,193, 5,600,099, 5,049,085, 5,876,215, 5,890,915 and related patents.
In addition to the problem, mentioned previously, of interconnection failure caused by gaps between contacts, an additional cause of interconnection failure occurs by occlusion of a metal contact due to surface contamination with e.g. grease, non-conducting particles or a layer of metal oxide. Such an oxide layer results from air oxidation of the metal. Since oxide layers generally impede the passage of electrical current, reliable contact requires removal or penetration of the oxide layer as part of the interconnection process. Several means for oxide layer penetration, towards reliable electrical connection, may be referred to as particle interconnect methods as provided in U.S. Pat. Nos. 5,083,697, 5,430,614, 5,835,359 and related patents. A commercial interconnect product, described as a Metallized Particle Interconnect or MPI, is available from Thomas and Betts Corporation. The product is a high temperature, flexible, conductive polymeric interconnect which incorporates piercing and indenting particles to facilitate penetration of oxides on mating surfaces. Another commercial, electronic device interconnection product, available from Tecknit of Cranford, N.J., uses xe2x80x9cHard Hatxe2x80x9d and xe2x80x9cFuzz Buttonxe2x80x9d contacts in selected arrays. U.S. Pat. Nos. 4,574,331, 4,581,679 and 5,007,841 also refer to the xe2x80x9cFuzz Buttonxe2x80x9d type of contact.
The previous discussion shows that interconnection of electronic devices has been an area subject to multiple concepts and much product development in response to the challenges associated with mechanical issues of interconnection and resultant electrical measurements. Regardless of advancements made, there is continuing need for improvement in three key areas, namely registration between interconnecting devices and electronic components, flexibility of contact sets for reliable device interconnection and minimization of the force required for reliable interconnection. In view of the continuing needs, associated with interconnect structures, the present invention has been developed to alleviate drawbacks and provide the benefits described below in further detail.
The present invention provides a compliant interconnect assembly for effecting reliable electrical connection between electronic devices, with contact forces much lower than previously attainable. Connection schemes, that include the compliant interconnect assembly, may be temporary for testing a semiconductor device that may be addressed via the conductive traces of a circuit used for e.g. test and burn-in.
In addition the compliant interconnect may be used as a contactor, a production socket, a burn-in socket, a probing device, a board to board interconnect, as a device to device interconnect and similar applications. The compliant interconnect is a low profile, rugged structure that forms solderless, releasable and remateable connections to delicate IC packages with application of low actuation force. Repeated cycling between connect and disconnect configurations, over extended time periods, demonstrates the remarkable durability and reliable electrical performance of compliant interconnect assemblies, according to the present invention.
More specifically the present invention provides a compliant interconnect assembly including a contact set and a compressible interposer to electrically connect a first electronic device to a second electronic device. The contact set includes an electrically insulating flexible film having at least one conductive contact suspended therein. Further, the flexible film has formed therein at least one de-coupling hole proximate the at least one conductive contact. The compressible interposer comprises an electrically insulating elastomer sheet as a matrix for at least one electrically conducting elastic column to provide a localized conductive path through the thickness of the elastomer sheet.
The compliant interconnect assembly is formed when the contact set lies adjacent the compressible interposer and at least one conductive contact engages at least one conducting elastic column. Electrical connection is made when the first electronic device and the second electronic device abut opposite sides of the compliant interconnect assembly preferably with an abutment force of less than 20 g per conductive contact.
The present invention further provides a compliant interconnect between a first electrical component and a second electrical component. Such a compliant interconnect comprises an electrically insulating flexible sheet having at least one conducting pathway therethrough and having formed therein at least one de-coupling hole, proximate the at least one conducting pathway.
A method for forming a contact set comprising a plurality of conductive contacts electrically isolated from each other comprises a number of steps after providing a copper plate having a first side and a second side. The first side has a plurality of islands of etch resist thereon and a pattern of protected areas of etch resist covers the second side. Application of etchant to the copper plate forms a plurality of engineered asperities on the first side of the copper plate and a pattern of posts on the second side of the copper plate. After removing the etch resist an insulating film, having an adhesive coated side, an exposed side and a plurality of holes formed therein, corresponding to the pattern of posts, is laminated to the second side of the copper plate, with the adhesive in contact with the copper plate, and the pattern of posts extending into the plurality of holes in the insulating film. Photoresist is applied to the resulting laminate over the first side of the copper plate and the exposed side of the insulating film before exposing the first side to a first radiation pattern and applying etch resist to areas of the first side of the copper plate exposed during development of the photoresist. After removing residual photoresist from the first side of the copper plate, the application of etchant produces a plurality of individual bumps adjacent to the adhesive covered side of the insulating film. Removal of etch resist reveals engineered asperities attached to individual bumps. Exposure and development of photoresist, on the exposed side of the insulating film, according to a second radiation pattern, produces openings in axial alignment with the pattern of posts and the plurality of holes formed in the insulating film. Deposition of copper on the pattern of posts forms contact tails protruding from the insulating film. Thereafter, removal of residual photoresist produces a contact set, according to the present invention, having conductive contacts electrically isolated from each other by the insulating film.
The present invention further includes a method of forming a compressible interposer comprising a plurality of conducting elastic columns electrically isolated from each other. The method comprises a number of steps after providing a composite sheet having a first spacer layer in removable contact with a second spacer layer removably laminated to both sides of an electrically insulative elastomer sheet. A plurality of holes is formed to extend through the composite sheet before filling the plurality of holes with a curable conductive fluid. After curing, the conductive fluid forms conducting elastic columns electrically isolated from each other. Removal of the first and second spacer layers provides a compressible interposer having conducting compliant projections extending on both sides of the elastomer sheet.
Terms used herein have the meanings indicated as follows:
The term xe2x80x9cStandard Pitchxe2x80x9d refers to a centerline-to-centerline separation of 0.8 mm to  greater than 1.27 mm between individual contact pads in a multiple-contact array.
The term xe2x80x9cFine Pitchxe2x80x9d refers to a centerline-to-centerline separation of 0.5 mm to 0.75 mm between individual contact pads in a multiple-contact array.
The term xe2x80x9cSuper Fine Pitchxe2x80x9d refers to a centerline-to-centerline separation of 0.2 mm to 0.4 mm between individual contact pads in a multiple-contact array.
xe2x80x9cPre-load actuationxe2x80x9d refers to the height reduction of a conducting elastic column produced when sufficient force has been applied to an interconnect assembly according to the present invention to provide reliable electrical connection.
xe2x80x9cPre-load deflectionxe2x80x9d refers to the height of a conducting elastic column under pre-load actuation.
xe2x80x9cPre-load actuation forcexe2x80x9d refers to the average weight applied to each contact point to provide reliable electrical connection.
xe2x80x9cFull stroke actuationxe2x80x9d refers to the height reduction of a conducting elastic column produced when sufficient force has been applied to the interconnect assembly to provide reliable electrical connection allowing for variation in contact/BGA planarity.
xe2x80x9cFull stroke deflectionxe2x80x9d refers to the height of the conducting elastic column under full stroke actuation.
xe2x80x9cMaximum or full stroke actuation forcexe2x80x9d refers to the average weight applied to each contact point to provide reliable electrical connection during full stroke deflection.
xe2x80x9cContact resistancexe2x80x9d refers to the electrical resistance contributed in the electrical current conducting pathway, by the interconnection assembly.
xe2x80x9cNumber of actuationsxe2x80x9d indicates the maximum possible number of make and break connections between an interconnection assembly according to the present invention and a target device.
xe2x80x9cDe-coupling holexe2x80x9d refers to an opening formed in a film or planar element or sheet to make the sheet more pliable. Removal of material between portions of a sheet reduces the influence that movement of one portion has upon the other. The portions have become de-coupled by removal of material. Incorporation of de-coupling holes (see FIGS. 1 and 8) in contact sets and compressible interposers, either separately or both together, provides more freedom of movement for individual conductive contacts and conducting elastic columns by reducing the direct influence of movement of the substrate film or elastomeric sheet respectively. De-coupling holes distributed around individual contacts or conducting columns as random or geometric clusters allow greater freedom and beneficial displacement of these interconnecting components.